This invention relates to an improved method for preparing tetra-lower-hydrocarbylsilanes in high yield.
Tetrahydrocarbylsilanes are useful in the formulation of hydraulic fluids and lubricants which are stable at high temperatures. Such tetrahydrocarbylsilanes possess excellent viscosities over a wide temperature range, low pour points, and exhibit excellent thermal stabilities. Processes for the preparation of various tetrahydrocarbylsilanes include Tamborski et al., U.S. Pat. No. 4,367,343 which provide a method for preparing tetraalkylsilanes by reacting a halosilicon compound with at least two organometallic compounds.
Onopchenko et al., U.S. Pat. No. 4,578,497 describe a process for the preparation of tetraalkylsilanes by contacting an admixture of at least one alkylsilane and at least one alpha olefin under an inert atmosphere with an oxygenated, platinum-containing catalyst under hydrosilylation conditions. In U.S. Pat. No. 4,572,791, Onopchenko et al. describe a process for preparing a mixture of saturated and unsaturated silahydrocarbons in high yield using a rhodium-containing catalyst in which such admixture contains at least 75 percent saturated silahydrocarbon. In Onopchenko et al. ('791), at least one alpha-olefin containing from 2 to about 20 carbon atoms per molecule and at least one alkylsilane selected from dialkylsilane, trialkylsilane, and mixtures thereof are contacted in the presence of a homogeneous rhodium-containing catalyst having a basicity substantially equal to or less than that provided by a rhodium-containing catalyst having a triphenyl phosphine ligand or a heterogeneous rhodium-containing catalyst.
Tetraalkylsilanes are produced by the process of Bakshi et al., U.S. Pat. No. 4,595,777 wherein a mixture of alkylchlorosilanes and trialkyl aluminum compound are reacted under alkylation conditions, preferably in the presence of an alkali metal salt. The reaction is conducted at a temperature from 150.degree. to 300.degree. C., preferably at elevated pressure of from 1 to about 100 atmospheres under an inert gas such that the more volatile components are kept predominantly in the liquid phase.
Lennon, U.S. Pat. No. 4,650,891 and U.S. Pat. No. 4,672,135 describes methods for preparing tetraorganosilanes by reacting a halo-substituted silane and an organomagnesium compound in the presence of a catalytically effective amount of cyanide or thiocyanate catalyst.
Particularly useful methods for the preparation of tetraalkylsilanes are described in Nelson, U.S. Pat. No. 4,711,965; U.S. Pat. No. 4,711,966; U.S. Pat. No. 4,845,260; U.S. Pat. No. 4,916,245; U.S. Pat. No. 4,973,724; and U.S. Pat. No. 4,999,447. U.S. Pat. No. 4,711,965 describes a process wherein an alkali metal aluminum tetraalkyl is reacted with an alkyl trihalosilane. U.S. Pat. No. 4,711,966 relates to the preparation of tetraalkylsilanes by reacting a trialkylaluminum and an alkali metal aluminum tetraalkyl with a silicon tetrahalide in a certain mole ratio. U.S. Pat. No. 4,845,260; and U.S. Pat. No. 4,973,724 relate to a three step process for the preparation of tetraalkylsilanes by reacting Na, Al, H.sub.2, and olefin in the presence of an organoaluminum catalyst to prepare an intermediate product, which can be reacted with a trihaloalkyl-silane to produce the desired product. U.S. Pat. No. 4,916,245 and U.S. Pat. No. 4,999,447 describe the preparation of tetraalkylsilanes by reacting an alkali metal aluminum tetraalkyl and an olefin with an alkyl trihalosilane.
Beard, U.S. Pat. No. 3,291,742, describes certain aryl aliphatic-oxy silanes which are useful as heat transfer media, hydraulic fluids, or lubricants, and which are stable liquids over a wide temperature range. In the process for preparing such aryl aliphatic-oxy silanes, an arylhalosilane is reacted with an appropriate alcohol. Other hydrocarbyl-oxy silanes are described in Askey et al., U.S. Pat. No. 4,141,851, and Ando et al., U.S. Pat. No. 5,039,555.
While the above processes are useful in preparing a variety of tetrahydrocarbylsilanes, there remains a need for an improved process preparing tetra-lower-hydrocarbylsilanes in high yields at more moderate pressures. The use of more moderate pressures greatly decreases the cost of the reactor and provides less operating difficulties.